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How can a pilot fly a descent angle of 4° in an A320?
Would any A320 pilot be able to share any tips regarding maintaining a descent rate for final approach of 4°? Of course this is in case of manual flying.
I know we can use a descent rate of speed*5 rule to assume we're on a 3° descent angle, but what if we need to descend 4° or even 5°?
Let's assume no wind and 60 tonnes weight of aircraft.
Lastly if we have a strong headwind or tailwind or crosswind, would the calculated rate of descent in ft/ min need to be adjusted?

It's great to ask questions, but it does scare me a bit that a pilot of a commercial aircraft as complex and large as the A320 may be asking piloting questions of random strangers (with unknown and undocumented qualifications) on the internet.  The Airbus A320 is commonly used by commercial airlines to transport passengers, and as a person who sometimes flies commercial, I hope there is training available elsewhere from official sources who are accountable for providing accurate answers.  This SE is nice, but there is zero accountability or guarantee of accuracy of any answer here.

@RockPaperLz-MaskitorCasket Pretty sure the OP flying using a desktop simulator and is not a real pilot. So it's perfectly fine to ask such questions here.

@Bianfable Ah, thanks.  Just curious, how did you come to that conclusion?  BTW, enjoy reading your posts.

@RockPaperLz-MaskitorCasket Based on previous questions and comments, e.g. this comment.

@Bianfable Good memory (or cross-reference)! I've seen so many errors published on the internet (including from "reliable" sources), that it concerned me that pilots may be considering this site as a place to receive part of their training.  I enjoy this site, but for pilots of real aircraft, nothing replaces real training by qualified instructors.  For those having fun on their home computers, as you imply, errors aren't going to cause any real problems.

This is a decent question, but often the question should be "how do I align to the glidepath", which is very different than following an arbitrary 4 degree path. Use of FPA or VS during landing has led to several incidents like Air Canada 614 or Indian Airlines Flight 605 when airspeed decreased too much or the pilot crossed the minimum descent altitude. Not to mention you may have to be fully configured at the FAF. FPA is nice, but don't use it if you want APPR instead.

@cody, your answer is somehow irrelevant and not useful to me. There's a reason why I asked 4°, it's because based on charts there's an approach with a 4° descent for a specific airport. Asking for tips if you can't follow instruments nor A.T.C. So if you don't have the answer no need to respond fuher.thanks.

@Bianfable I think the concerns showed from first commenter is of real concern.
https://edition.cnn.com/2020/06/25/business/pakistan-fake-pilot-intl-hnk/index.html
There are countries that have more reliable internet connection than flight authorities...

@Bianfable. Can you please explain where the 101 comes in the tan calculation? Would be great to provide the detail please. Everything else is understood

@RO That is the conversion factor for knots into feet per minute: WolframAlpha

You're in luck: the Airbus A320 flight director has a special mode for exactly this: TRK/FPA (track and flight path angle):

(image source)

When you are on final approach, press the HDG V/S - TRK FPA pushbutton on the FCU. This changes the HDG (heading) selector to TRK (track) and the V/S (vertical speed) selector to FPA (flight path angle). It also changes how the flight director is displayed on the PFD:

Flight Path Director (TRK FPA selected on the FCU)
The display is an alternate way of transmitting flight director commands.

The Flight Path Vector (FPV) symbol illustrates the track and flight path angle actually being flown.
The Flight Path Director (FPD) symbol shows the pilot how to intercept and fly the vertical and lateral flight path defined by the FMGC. When the pilot superimposes the FPV and FPD symbols, the aicraft is flying the commanded trajectory.

(Airbus A320 FCOM - Autoflight - Flight Guidance - Flight Director)

Now select the final approach course on the TRK selector on the FCU.

Then select the desired flight path angle (in your case -4.0 for a 4° descent angle) on the FPA selector.

The flight director will now compute how to stay on the track and descent path, taking all head-/tailwind and crosswind components into account. There is no need to manually calculate what vertical speed is required.
You can also engage the autopilot (or keep the autopilot engaged) and it will follow the flight director guidance. If you want to fly manually, just follow the FPD commands on the PFD.
Note that flying in this mode is usually not required for a non-precision approach (except a LOC approach, which should be flown with LOC and FPA modes) because managed modes are recommended when available:

Managed modes are recommended, but selected mode might be useful in case of system or equipment failures.
It is worth recalling that in selected mode, the Flight Path Angle (FPA) easily permits to follow the published descent gradient, but the pilot must still ensure that the vertical trajectory relative to the touchdown point is precisely followed.

(Airbus - Safely Flying Non-Precision Instrument Approaches)

For an aircraft without FPA mode, you can estimate the required vertical speed based on your ground speed (sketch not to scale):

From basic trigonometry, we know that
$$ \tan(\alpha) = \frac{\text{VS}}{\text{GS}} \quad \Leftrightarrow \quad \text{VS} = \tan(\alpha) \text{GS} $$
You probably don't want to use the same units for GS and VS, so with typical units and $\alpha=4^\circ$ we get
$$ \frac{\text{VS}}{\text{ft/min}} = \tan(4^\circ) \frac{\text{kn}}{\text{ft/min}} \frac{\text{GS}}{\text{kn}} \approx 0.070 \times 101 \times \frac{\text{GS}}{\text{kn}} \approx 7.08 \frac{\text{GS}}{\text{kn}} $$

That article sounds like a direct response to Air Canada FPAing a plane into a hill. Note the -3.5 degree angle in that approach.

Thank you for the detailed response. But what if F.P.A and instruments are not available, and you''re only left with your altitude and distance from TDZE? For a 3° descent I know I can use my IAS to determine my rate of descent to maintain a 3° descent but I'd like to know if there's any such thing for a 4° or 5° descent?

@RO If you have that much instrument failure, you have bigger problems! You need ground speed (GS), not IAS to do this calculation. I added a section to the answer to show how to calculate VS based on GS.

Hi there, thanks again. I appreciate all your detailed answers which are perfectly understandable. Just 1 further    question please using trigonometry is absolutely great, but any shortcut just like for a 3° descent we take GSx5 to get the rate of descent in ft/min? And to reassure everyone, I'm not a pilot, neither a student for being a pilot, just a MFS2020 startong 1 year ago and enjoying understanding how all this works.thanks again

@RO See the last formula: for 4° you could use GSx7. For 5° just plug in tan(5°) instead and you'll get something like GSx9.

Perfect many thanks. Your answers are the best

Sorry but one more thing. On a 3° dsscent angle, I can esrimate that I will be on profile and that I need to be at 3000 ft if my TDZE is 10NM from my position (×3 rule). How do I apply this with a 4°  descent angle?

@RO You can use the same triangle I show in the answer, except with distances instead of speeds. Just multiply the distance with the tangent of the angle to get the altitude: example on WolframAlpha

sorry again, trying to understand in real life. I'm landing at FIMP RWY 14 with a visual approach (no ATC no F.P.A). From charts, need to be at 4000 ft at BIGARA, 10NM from DME IPL which sems to be at TDZE. Graph says to initiate a 3° descent until  CUREPIPE, 8 DMZ IPL where the descent angle is 4° from there. Thre is terrain before BIGARA so let's assume this is an alt constraint. My goal is to go for a Constant path angle to TDZE. RWY 14 is at 183 ft. Assuming crossing TDZE 55 ft, means from 4000 ft I need to lose  3762 ft to TDZE, and need to start descent 4° at 3.7x4=15 NM? terrain ahead?

Hi there, a real pilot told me that we can't really use this approximation using trigonometry if we're on approach, i.e < 15 NM to landing. Using this method to determine whether you're on profile is between 15-50 NM to landing. My question is then how would you as a pilot get that plane down if you're at 4000 ft at 10NM from TDZE and no ATC, oi F.P.A mode? You must be trained to face instrument failure right? Any tips on how any of you pilot would do?


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M.D.A and distance from runway
Is there any standard distance from runway that corresponds to M.D.A for airliners?
I mean is there a rule or pattern as to a typical distance from runway where M.D.A is reached? Example 2.5 NM from RWY corresponds to your M.D.A?

Reached. Is there a typical distance from RWY TDZE that M.D.A should bz reached,. I.e at around 3.5 or 4 NM from TDZE, you normally should have reached  the M.D.A? On another topic, can you help regarding the case of circle to land if A.P is off for LFMN 04R? What would be the procedure in such a case?

There is no standard or typical distance for reaching the MDA. It depends on a lot of factors:

Where exactly is the descent from the platform altitude initiated?
How steep is the descent?
How high is the MDA?

All of these could be different depending on the approach and how the approach is flown.
For example, let us look at two non-precision approaches into runway 34 at LGKR:

The VOR approaches have an MDA of 2000':

This approach should be flown as a CDFA, where the descent from 2900' is initiated at 7.9 NM from the runway at an angle of 3.4°. This would result in reaching 2000' at ~5.4 NM from the runway.
However, when descending already at the FAF [FD34], which is 8.1 NM from the runway, you would reach 2000' at ~5.6 NM. If you would further change the descent angle to the standard 3°, you would reach 2000' at ~5.3 NM.

The RNP approach to the same runway has an MDA of only 770':

Here you fly the CDFA from a stepdown altitude of 1700' at 3°, resulting in reaching 770' at ~2.3 NM from the runway.

Formula for calculating the distance to the runway where MDA is reached:
$$ \text{MDA Distance} = \text{Start Distance} - \frac{\text{Start Altitude} - \text{MDA}}{\tan(\text{descent angle})} $$

Thanks. Does this work even if approach is not in straight line. Coming back to my visual approach on LFMN04R where I start my descent with F.P.A 3° radial 354 to CGS vOR and turning to final 43°. And lastly, can we talk about circling approach if AP is off? I'd like to understand if we're visual and use MDA set for precision approach to do a circle to land when AP is off makes sense and whether it's possible

Let's not mix different topics, please. In general, this formula will only apply to straight approaches. Otherwise, the direct distance to the runway is not the same as the actual flight path length. However, the first part of the answer still applies to circling approaches.

Can you give an examlke for the calculation? Distance is in NM and altitude in feet so I'm not able to make the conversion.

source: Stack Exchange

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A320 Level change autothrust variable speed
Have some questions I'd like to get a better understanding:

assuming at Vmax 32000 feet, autothrust on but speed selected at 340 knots or vmax on a320, and I get asked to climb quiclly at 35000 ft due to weather or any other reason. How to handle that without getting overspeed? Should I decrease speed and keep AP and Autothrust on? Autothrust mct or toga?What's the best approach?
same as above but on case of TA/RA to climb, meaning AP needs to be off.
on climb aftet takeoff before reaching TOC, if I need to climb much faster at my TOC, should I manually reduce speed and then increase vs? What about autothrust setting and whether it should be left on or off?

I assume this is flight simulator as most of this would be addressed during your type rating course, so the validity of my answer is depending on the fidelity of your simulation.

at high altitude you should not be able to fly Vmax because the speed is limited by mach number. But as a general rule you will not have a problem with overspeeding as you climb. So keep AP and ATHR on as you climb. AP will keep the selected speed as you climb. You can increase your climb rate momentarily by reducing your speed slightly. With MCT or TOGA autothrust will disconnect and you will not get any additional thrust beyound CLB at high altitude anyways.
If you get overspeed warning during climb while maintaining airspeed (like Vmax) it is because you are exceeding the MMO (Mach .82) during climb. Correct technique is to keep constant airspeed as you climb (around 300kts) until your mach number reaches planned crusing speed (around M.78) and then fly constant Mach number and let the indicated speed decay.

In TCAS RA both AP and flight director must be switched off but ATHR should be kept on. This forces ATHR into speed mode (indicated by ”MACH” or ”SPEED” on the top left corner of the PFD)
As you manouver, the ATHR will adjust the thrust to maintain current speed.

You get up quickest by using CLB or OP CLB mode with ATHR on. The climb rate depends on your airspeed. You get the steepest climb with green dot speed or fastest climb with Vy which is slightly higher, around 270kts or so depending on the weight. Momentarily you can increase climb rate by reducing airspeed but from takeoff to cruising altitude stick to Vy speed. This also correlates more or less with managed speed with Cost Index 0.

If you haven't read it, you might be interested in the NTSB report on the CRJ200 Pinnacle Airlines service ceiling incident where they stalled the thing out with a double flameout, eventually deadsticking behind some houses a couple miles short of the airport. For reasons nobody can fathom, they did the last several thousand feet of the climb in VS mode, basically forcing a zoom to get to FL410 and finding themselves there on the back side of the PC, the AP holding the alt as the speed bled off until the shaker went off and all hell broke loose. Then they lied to ATC about their situation.

@JohnK Luckily the flight envelope protections on the A320 should prevent such a situation here (not that I'd recommend trying such shenanigans).

@Bianfable Well, Airbus might prevent the consequences. It will not prevent stupidity.

@busdriver Much was made of taking it to FL410, the SS. The 200 when heavy doesn't much like to go above FL370 or so.  But the airplane was on a ferry and was empty. Had they let it climb in Mach mode and let it take its time and paid attention to their energy, they'd have been fine. The introduction of high altitude stall recovery in sim training, with the aggressive push over to dive instead of teasing it on the edge of shaker you do when low (non FBW), was the direct result of that incident. Lots of pilots didn't understand that the upper FLs are a very dangerous place.

@Bianfable Watching enough of Mentour's vids, I was surprised at how many incidents were seemingly made worse by the automation, because the crew were saturated, weren't aware of all of the ins and outs of the system, and there thus surprised, when, say, the  thrust levers start moving unexpectedly on a missed b/c some mode was mis-selected in all the confusion. I often wonder where the automation should stop.

Hi there thanks so much. Sorry I'm not a pilot and indeed for sim purposes. But if for instance you have already reached alt* at 32000 feet cruising at 0.80 mach assuming you had a C.I 100. Then if you're expected to climb rapidly to 35000 feet, how you do that without exceeding speed limit?reducing the speed would it not take you longer to climb?

Is it good to say that there might different resolution actions for FL change depending on whether you are climbing, i.e THR Climb, or whether you are already at cruising altitude, ALT*, i.e SPEED mode? If so can you summarize the actions for these 2 scenarios, i.e climbing and when already in cruise? Also if your  cruise Level is low say 15000 ft, does that change anything if you need to climb fast? What about for descending before TOD? Are these rules reversed?

@RO Well, usually there is not much you can do when climbing from 32000 to 35000 ft, ie. in high altitude. Just put the new altitude in and press the knob to activate CLB mode. This forces thrust to maximum climb thrust. If you need to expedite select a lower speed. This will trade speed to altitude while keeping engines at climb thrust. In decent to process is indeed reversed. Put the engines to idle (usually done by using on of the descent modes with AP and ATHR) and then keep your cruising Mach (f.ex. M.80) until your speed has increased to around 300kts. Then maintain that with idle power.

Thanks, and from 15000 ft at mach 0.80,  to expedite climb to 32000 ft, same I guess, not much margin right?

At 15,000' MSL and Mach 0.80, you're probably way, way above your VNE max indicated airspeed limit... Using 626 knots as the speed of sound at that altitude (standard day), 8/10ths of that is 500 knots -- yeah, your A320 isn't going to be doing that any time soon!

Ok but the question would then rather be what action is needed of asked to climb fast if asked to by ATC from 15000 ft given that I'm am already flying at max mach speed for that flight level.

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Where can I find airport diagrams for the Philippines?
I would like to have airport map, just like the one that pilots can see when they are taxiing. Is it possible to get such a map, even if you are not a pilot? Perhaps there are applications which a person can use to simulate taxiing on specific runways?
I am interested in Manila airport (MNL) and Mactan-Cebu airport (CEB).
Something like this:

resource location is off-topic as defined by the (help center)[/help/on-topic]. You may rephrase your question such that it ask for what you are looking for, the answer being likely to give you links to relevant resources.

The easiest way is to type the IATA code into Google along with "airport charts". The PDF you are looking for will be high in the search results. Here are the diagrams for Manila and Cebu.

Is there also some kind of application where you can simulate taxiing on selected airport?

www.proflightsimulator.com


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How do I choose the correct NACA airfoil for my requirements?
How do you find the correct NACA airfoil to use when you already know the requirements?
All of the research I have done on this has shown how to determine what kind of camber/chord/aspect ratio etc. only, but not how to actually pick the proper NACA airfoil. I would like to know if there is some website or program where you can easily find the correct airfoil given different circumstances. Then I would be more sure of having the correct airfoil when performing my tests. I understand I could just eyeball it, but I would like to be able to find the exact lift that my wings would produce, and that would only come from knowing the exact NACA airfoil.
It doesn't necessarily have to be a NACA airfoil, but it should be some type of airfoil where data can be taken from it.
I also could be approaching this from the wrong way, as I do not have an experienced mentor, so if using NACA is unnecessary or outdated please let me know because I really am at a loss of how to select the proper airfoil.

So basically you want to search airfoils based on camber/chord/aspect ratio?

I don't know of a reverse lookup program but if you have already decided on performance characteristics then there is a program that can modify airfoils to meet your characteristics using genetic algorithms. Google "xoptfoil". It uses xfoil as its back-end

Related questions: here, here, here. There are various links in those questions and their answers to tools, documents etc.

So you know your wing planform and look for the right airfoil.
You need to be more specific with your requirements, and yes, NACA airfoils will most likely not be the best choice. But since there is plenty of literature on them, they are a good start.
Please answer those questions first:

What is the maximum airfoil thickness you can afford? A thicker airfoil makes for a lighter wing with more internal volume for flaps and fuel. However, if you want to operate your design at high subsonic speeds, thickness needs to be controlled.
What is the lowest cruise lift coefficient and the highest lift coefficient for a clean wing and with flaps down? Does your design need flaps at all?
If the aircraft is small: What Reynolds number is flown at which lift coefficient?
What is the desired stall behaviour? Docile (as preferred for training aircraft) or snappy (as preferred for aerobatic aircraft)?
What construction technique is used for the wing? Wooden frame and fabric? All metal with countersunk or exposed rivets? To be built on a jig or on a flat table? Composite, in a mold or positive over a foam core? All of them have subtle consequences for airfoil selection.

Generally, you look at all requirements and then select or design the airfoil according to the desired pressure distribution at different angles of attack and Mach numbers. Once you tell us more, I can become more specific.

Hi, I have exactly the same question as OP and am building my airplane out of foam in order to experiment and have a better understanding of the different configurations and so. Reading aviation litterature helps a lot so far.  I therefor answered the questions above and would love to know what you would suggest: 1) 3mm 2) 1.200kg (= +/- weight of aircraft without engine) ->  lift coefficient $C_{L} = \frac{2mg}{\rho V^2 S} = 1.15$ - not sure flaps are needed, but I think adding flaps that can be oriented eg downwards helps during takeoff (that way at least chancs are higher my plane will fly)

yes is small - I think my Reynold's number is 211,164 assuming a velocity of 10m/s, chord with of 0.3m and (a guessed) kinematic viscuosity of 1.4207E-5  4) docile 5) foam - cut with light eg electric saw... - cut on flat table.

Conclusion: I would choose an airfoil +/- like this: http://airfoiltools.com/images/airfoil/ag11-il_l.png or http://airfoiltools.com/images/airfoil/ag37-il_l.png
Simply because the bottom seems to be flat and thus much easier for me to make in my home lab, but further than this I got no clue about what thickness I would need nor what minimal wingspan (maximum 1.3 meter) I would need.
I am learning this on my own by reading various books about aircraft design, so I may have made some mistakes. Feel free to correct or tell me if something of what I said looks weird or incorrect.

What would you choose based on my answers on your questions? EDIT: maximum airfoil thickness is not 3mm but 30mm. I can't edit any more.

@LandonZeKepitelOfGreytBritn: So your relative thickness is 10%. You will need more camber than the two airfoils you selected if you want to fly at a cl of 1.15 at such low Re numbers. A quick search shows the S3410 to be quite good (see here: http://airfoiltools.com/airfoil/details?airfoil=s4310-il#polars).

I used this website to compute the Reynolds number: http://airfoiltools.com/calculator/reynoldsnumber. According to Wikipedia the formula is $Re = \frac{ uL}{v}$. To me it isn't clear what I should modify at my airplane itself in order to get a higher Reynolds number and thus need less camber. Because * at first sight* the bottom side of the airfoil you linked seems pretty straight as well and I don t know whether I 'll be able to cut out the airfoil that accurately as this is the very first time for me. What practical thing can I do to increase the numbr and thus use a flattr foil?

@LandonZeKepitelOfGreytBritn: A higher Re does not imply less camber; I choose the higher camber because of the high lift coefficient. To increase Re you either fly faster or increase chord. I selected the S3410 due to the almost straight bottom; if you build it straight you will be close enough.

Are you sure LandonZeKepitelOfGreytBritn's relative thickness is 10%? I would say 23%. I don't know whether it really matters for the airfoil choice: (30mm/130cm)*100 = 23%

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Could the V-22 Osprey be used as a close air support platform?
I saw the US was looking for a new close air support plane. Why do they not use the V-22 Osprey? It is able to travel slowly and could carry more weapons than an A-10, for example.

The V-22 is a transport aircraft, not a close air support one. The V-22 was only recently even given weapons, and is highly limited to how much it can carry.

@ron beyer by volume it could carry what the a 10 (gau 8) does with modification maybe more. It would need modification but it would be cheaper than making a whole new plane.

The V-22 is a transport aircraft, not a combat one. It is fragile and not very manoeuvrable.

You seem to be asking quite a few questions of the form "Could System A be repurposed to completely different Function B?" The answer to any such question is "Maybe, in principle, but that would be a really bad place to start from, since System A was designed to do something completely different from Function B." This isn't a particularly productive sort of question to ask.

Okay, the answer to this question is a pretty clear "no way, no how, not even close," but that doesn't make the question itself not worth keeping around.  This isn't "opinion" like a "which is better, the X or the Y", and it's quite clear what's being asked.  And the answer below is a good one with objective reasons why this idea wouldn't work out well.  Voting to keep open!

@RalphJ So are we going to have one of these questions for every combination of plane and repurposed role? We've already had SR-71/business jet. Now, Osprey/ground attack. What next? A-380/fighter? CRJ700 /refuelling tanker?

@DavidRicherby You say that as though passenger airplanes have not been used before in an offensive role, or that it is trivial and not worth discussing.  Very tempted to open a question along those lines but I don't want the downvotes :P

@DavidRicherby It's a good question to ask if you don't understand "why not?". Maybe "Could an old prop-driven cargo plane (C130 or something equally ridiculous) be turned into the very embodiment of death from above, able to drive fear into the heart of the enemy?" would be an equally useless question.

As the OP suggested using the Osprey, my immediate thought was that he had it in mind as a replacement for the old magic dragon: https://en.wikipedia.org/wiki/Lockheed_AC-130. (I assumed they mentioned the A10 purely to say that - in their opinion - it couldn't take on Puff's job.)

The V-22 is not without its strong points as a support aircraft.  However, CAS is a specialized role for which it will never truly be ideal.  That's not to say it wouldn't be feasible to deliver weapons with one, once modified appropriately.
The good news is that you could likely bring it up to roughly attack-helicopter levels of armament.  I estimate you'd get roughly AH-1 levels of firepower, but with a transport capability and over significantly longer ranges.  Essentially, you'd end up with a sort of modern, squishier version of the Mi-24.
The squishiness is a significant concern though.  Compared to virtually any rotary wing platform, the V-22 is large and loud.  It's easier to acquire by sensor, by sight and by ear.  It's also not particularly resistant to ground fire.  In that sense, it bears some of the some limitations of UH/CH platforms or "C" class fixed wing A/C.
In that sense, a weaponized Osprey is actually competing to be a newer-bigger MH-60L Direct Action Penetrator.  You could also view it as an update to AC-47D (Puff the Magic Dragon).
There is certainly a niche there, but as a general purpose, high performance, ground attack A/C it falls short.  As noted above, external stores would degrade performance and there would be limitations imposed by the airframe concerning capacity.  When you start taking weapons off the table, you start limiting capability.  The speed, altitude and maneuverability of the platform will never be ideal for integrating into fixed-wing A/C formations, nor will they confer the ability to out run or out fight even the most outdated of adversary fixed-wing A/C in an unescorted role (an A-10, for example, is more than an match for a V-22 air to air).
My verdict:
- Viable long range, rotary-wing, general purpose support/strike platform
- Not a true/ideal replacement for fixed-wing CAS capability

Can it be? Sure.
Let's take a look at what it would be replacing.
The A-10 was designed from the ground up to be a platform for moving the GAU-8 into range of the target.

It has good low speed flight characteristics.
The engines are mounted high and to the rear to protect them from FOD (both debris kicked up by the GAU-8 and hostile weapons fire).
The cockpit is within a 540Kg titanium armored tub to protect the pilot and critical flight systems.
It has wing hard-points for carrying additional munitions should the GAU-8 not be sufficient for the current mission.

Why won't the Osprey be adapted for CAS?

Because it travels slowly, it's susceptible not only to MANPADS and other traditional AA systems, but simple small arms fire becomes a threat.

For example, the Douglas A-1 Skyraider (which the A-10 replaced) - a "propeller-driven design was also relatively slow and vulnerable to ground fire. The U.S. Air Force and Marine Corps lost 266 A-1s in action in Vietnam, largely from small arms fire." (Source, emphasis mine)

Those huge props (38' diameter, which is smaller than the optimal 43' (Source)) are a very vulnerable target - damage to them may make the aircraft unflyable.
Hits to the engine rotation system that may not cripple the aircraft may cause it to have to land with the props in the vertical plane instead of horizontal. They're designed for this without destroying the rest of the aircraft, but that means thorough inspections and expensive prop replacement prior to its next flight.
It could have an armored cockpit surround retrofitted, but it's not designed for it.
It could have hard-points mounted, but they would need to be integrated with this swing-wing mechanism which would significantly increase the design/build cost and complexity

The swing-wing (used for stowing the plane on a carrier) could be eliminated, but that would defeat one of the main uses of the aircraft.

It's highly likely that the replacement for the A-10 (current thought trends toward the F-35, but that's contentious) will be more similar to the A-10 itself. That kind of role has some unique requirements that can be fulfilled by a more multipurpose aircraft, but not as well.

Wow, I appreciate the check mark, but you may want to wait a bit longer to see if anyone else has something good to contribute, as well.

And at the end of the day, you'd have a CV-22 modified into a semi-replacement for an AH-1 (roughly speaking) -- a helo-ish aircraft replacing a helo.  But it wouldn't replace the A-10, which still has jet motors rather than props, can go much faster, pull more G's, fire a massively bigger gun (without destroying itself), and drop stuff that the CV-22 never could.  This is a good answer explaining the issues (read, costs) involved to convert the Osprey into an attack platform... although it wouldn't be an attack platform much like the A-10, even then.

@RalphJ Given that nothing will be able to replace the unique capability that is the A-10 -- go back to the requirements creation and work forward -- comparing anything to it is an exercise in futility.  This answer does a nice job of walking the dog on the speculation of CAS/V-22.

The V22 will be contributing as a CAS platform for the USMC along with KC130s until the service finds a suitable platform to replace the A10. Marines are actually running out of fighter jets. At this point, only about 87 of its 276 F18's are serviceable at any time.
For any flying arm, roughly 30% availability is really bad! And the A10 cost \$20,000/hr flight time and is increasing constantly because of the aging of the airframe. The services gambled with the F35 and lost, so until the F35 is combat worthy or is scrapped and a suitable replacement is found for CAS role, the under-funded marine corps is making due with what they got.
The Harvest Hawk modification kit for all the services KC130s, adds an electronic jammer, a Target Acquisition and Designation System, and hard-points. Load-outs have featured as many as four AGM-114 Hellfire and ten AGM-176 Griffin missiles. They’re hardly as sophisticated and capable as AC-130U/W/J gunships, but the modular kits cost far less(\$10 million vs. \$200 million).
The Osprey’s weapons kit is less defined. With hard-points for targeting equipment and laser-guided missiles—APKWS or Viper Strike. And they will be capable of such functions, though just as DanS said, "albeit with less effectiveness".

CAS, no. Mini-gunship, firing standoff weapons in coordination with marines on the ground, quite likely will happen.  The V22 should be able to substitute, albeit with less effectiveness, any role the C130 performs for the marines(cargo, tanker, gunship, ISR).  There will be scenarios where C130s can't get to the airspace but V22s are embedded with the MAGTF and will always be there.

Welcome to aviation. Would you mind expanding some of the points? you make several claims that to me seem hard to believe. Can you back up some of your assertions?

The V-22 is a lot less capable in this than the C-130. It's smaller, less stable, and has a far smaller effective payload. Where the C-130 can fit a 103mm howitzer (not sure whether the Marines have that variant) the V-22 is limited to miniguns and heavy machine guns.

@jwenting AC-130 has a 105mm.  The Marines still use a 105mm in the field, M119A3, as of last year.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Where can we fly a drone in Paris?
I'm wandering if I can fly my Phantom 4 Pro in Paris. What are the restrictions? If it's not allowed, can I get an official authorization as I'm an experienced drone operator?

Google? My french is very rusty but it looks like there's plenty of information regarding drone flight in Paris, e.g. here. And there's even a festival.

Here's a general government guide. I can't answer your question about Paris specifically, but the guide isn't encouraging: no flight is allowed over built-up or sensitive areas (including monuments and parks), or in restricted airspace (which covers most of central Paris). If no one here has any local knowledge, you might look for a local club that could inform you about it.

As Paris is a prohibited airspace at low altitude (P23 up to 6,000 ft), a drone cannot fly within it. The text of the préfecture de police related to drones, and the link to the DGAC instructions. Here is the official map of the restricted areas. You may contact the PP.

@mins thank you for your comment, I'm a bit confused, in the map restricted areas the Seine river seems to be purple and not red, does this mean I can fly my drone over the Seine at 30ft altitude ? thank you again

That's not clear to me, as it seems there are two overlapping areas. But P23 also includes water areas. You may directly contact the PP, or as others also mentioned the Férération d'Aéro-Modélisme. That's what I would do (I'm living close to Paris). If you intend to fly for some time, a club will provide an assurance with the license, it may be a good deal and will save you the time to understand the regulation, specially now with Vigipirate active. I think a month ago flying over the Champs-Elysées was possible on a week-end, but that's a temporary exception.

Another useful information: This map shows two "annexes": I is the no-fly (all regulated airspaces) and II for specific areas (hot spots) where altitude is regulated. As you can see annexe I covers a good portion of Ile de France.

Seem's like there no way to fly drones in the hole Ile de France area .. quite sad ... have to take the train and travel far ..far away to do what I love :/

There is a restricted zone over Paris known as LF-P 23 Paris.
NO ONE (planes, helicopter, drones, broomsticks...) can fly over Paris from the ground to 6500ft... unless you have a special authorization, which you will not get for flying an amateur drone just for fun.
This zone is defined by the Arrêté du 21 février 2018, click the link if you are interested in the technicalities.
Personal experience: the only drones I ever saw flying here were the fire department ones during Notre Dame's Cathedral's fire and during the July 14th fireworks, for the official video broadcast along with police helicopters with TV crews on board.


text:
Is this Part 23 Final Rule document the final regulation and what are the main improvements?
Is the FAA's new Part 23 Final Rule the final new Part 23 document? Or will another document be released? The formatting is totally different and kind of a discussion can be found in all the paragraphs.
Also, what are the main improvements in this new version of Part 23?

The document contains no effective date, so it clearly can't be the final version.

The document itself is final, but it isn't the same thing as the actual regulations.
The same thing happened with the recent part 107 UAV regulations: the final rule document came first, then the regulations were published later. That means, at some point soon (?) the part 23 regulations will be updated to include the final rules you found, but I have no idea exactly when that will happen. The Part 23 final rule itself says:

DATES: Effective [INSERT DATE 8 MONTHS AFTER DATE OF PUBLICATION IN
  THE FEDERAL REGISTER].

AOPA has a good explanation of what the rule changes will mean.


text:
What is a "round-robin flight", in layman's terms?
I'm struggling to find a sufficient explanation of a round-robin flight, as it pertains to ATC.
Can someone explain, in layman's terms, what it is and the lifecycle of a round-robin flight? Graphic analogies are welcome.

A round-robin flight is when you start from airport A, go to airport B, and then return to airport A with a single flight plan. It seems to be a problem sometimes for FAA ATC because of the intermediary airport not being the end of the flight. Read Round-robin IFR flight plans

It's simply a flight that returns to the original airport after stopping at one or more other airports.  ATC doesn't have a good way to code those types of flight plans in the computer, so the pilot will usually just tell the controller that he/she is planning to land at the intermediate stop for x amount of time.
The controller will then either close their flight following (or IFR clearance as appropriate) and have them reopen when they take off again, or just keep it open.  It depends on how busy their airspace is.  Often they'll just leave it open if it's in the middle of the night.


text:
How do military fighter aircraft identify themselves and each other?
I live in an area where there is much NATO military activity. Often there are various fighter aircraft fly-overs. But none of the common websites such as flightradar24, flightaware and planeflighttracker etc. used for identifying aircraft using ADS-B and ACARS etc, are able to "see" them.

So apart from ground radar, how does the military aircraft identify themselves?
Are there other type of transponders used in these?
Has there been any known attempts at building some amateur radar network to track these unidentified aircraft?

There was little useful information in this SE answer. I also found after posting a very similar SE question and answers. However, it still doesn't fully address the questions.

EDIT: As an update for question (3), there seem to have been some success on using SDR's as passive radars, as shown in these links:

http://www.rtl-sdr.com/building-a-passive-radar-system-with-an-rtl-sdr/
http://www.rtl-sdr.com/tag/passive-radar/
http://www.kaminski.up.lublin.pl/RTL-SRD.html
http://hackaday.com/2015/06/05/building-your-own-sdr-based-passive-radar-on-a-shoestring/

What makes you think something other than ground radar is needed? Ground radars (mainly SSR but also PSR) are used to track the large majority of all flights today, mostly based on mode A/C and mode S transponders.

As for amateur radar networks, you have to be a filthy rich "amateur" if you want to install one of these in your back yard: http://www.radartutorial.eu/19.kartei/14.ssr/pic/img3091.jpg

The civilian SSR transponder (mode 3/A, 3/C or 3/S) is derived from the military one (IFF) which is being upgraded to Mark XII. IFF has 5 interrogation modes, mode 3 is the civilian mode. When you mention amateur radar network, I suppose you mean transponder receiver network like ADS-B receivers used by the sites you list in the question, not the SSR stations with directional antennas.

I think the latest update is to Mark XIIA according to STANAG 4193 it seem to use 1030 MHz (ground-to-surface) interrogation and then 1090 MHz ADS-B (answer).

A surprisingly good source for the different modes used.

Related

"No, no, don't shoot me, you idiot - I'm your wingman!"

Military aircraft, like civil aircraft have transponders. Military aircraft  are assigned military codes, and their transponders have special military modes.
An aircraft doesn't need a transponder to be "illuminated" by radar, but the transponder enhances the "blip" and modern transponders transmit additional aircraft information such as altitude (Mode C).
See the "Interrogation Modes" of transponders in this link.
Notice that the Military modes include "cryptographically" secured version of Mode S and ADS-B GPS positioning.

I believe the secure mode is called Mode 4, if I remember correctly.

@Steve correct, and also Mode 5, which has Mode S and ADS-B GPS position information.

Seem that Mode 4/5 are also waveform based.

@not2qubit as opposed to PCM?

@Devil07 Yes, I suppose, since it is considered a NATO secret and not officially mentioned anywhere, while every product brief mention "waveform". I take it to believe they are using some more common way of spread-spectrum modulation such as: Frequency-hopping spread spectrum (FHSS), direct-sequence spread spectrum (DSSS), time-hopping spread spectrum (THSS) or chirp spread spectrum (CSS), as they provide greater resistance to narrow-band jamming.


text:
Is there a solution to radio interference?
I was reading about the Tenerife Disaster and came across what seemed to be the  probable cause behind the accident.

A simultaneous radio call from the Pan Am crew caused mutual interference on the radio frequency, which was audible in the KLM cockpit as a three-second-long whistling sound (or heterodyne). This caused the KLM crew to miss the crucial latter portion of the tower's response. The Pan Am crew's transmission was "We're still taxiing down the runway, the Clipper 1736!". This message was also blocked by the interference and inaudible to the KLM crew. Either message, if heard in the KLM cockpit, would have alerted the crew to the situation and given them time to abort the takeoff attempt.

https://en.wikipedia.org/wiki/Tenerife_airport_disaster
I understand that the science behind radio waves is the cause for this interference, but is there a solution (non-radio if need be) for when ATC and other aircraft talk over each other?
edit1: By solution I mean a way of only allowing 1 party to speak on a specific frequency at a time , be it technical or not. I would just want the possibility of pilots/ATCs talking over each other to be close to 0.
edit2: I know the Tenerife disaster was caused primarily by the pilot's inability to wait for clearance, and then report it back, but this question is about radio interference and if a solution exists, not if fixing radio interference is a worthwhile task to begin with.

What kind of solution do you mean?

@fooot, By solution I mean a way of only allowing 1 party to speak on a specific frequency at a time , be it technical or not. I would just want the possibility of pilots/ATCs talking over each other and not being able to hear to be close to 0.

Okay, "A" and "B" both go to key their respective microphones at the same time.  What do you envision should happen?

@RalphJ, Maybe a way of preventing A and B from ever dispatching at the same time in the first place (similar to a semaphore in software)? I just want to know why there is not a solution for this problem that has cost many lives.

@mins, Why is it considered not usually a problem? Even when some of the biggest disasters could have been prevented if talkover was not a thing?

@mins, I have found that these standards were increased greatly after this incident. I am still wondering if there lies a technical solution.

The problem was caused by the fact that VHF communications use amplitude modulation, the carrier wave is not suppressed unlike in single side band modulation. When there are two or more transmitters operating at the same time,  this will yield a strong interference tone that has as its frequency the difference between the frequencies of the two transmitters (they are never exactly the same, so, 200 hertz off means a 200 hertz tone). HF communications use single side band modulation where there is no carrier wave, this allows for multiple planes to talk simultaneously.

VTR. This question is perfectly answerable by talking about means of communication in operational aviation. Explain simplex radio, explain CPDLC, and explain why new equipment in a global industry can't just be implemented from one day to the next.

@J.Hougaard: As it is now, the question is only about interferences between voice transmissions and existing solutions. I voted to close it as it is a broad topic that doesn't fit the site principle of "a best answer" can be determined. Many solutions exist in the data/voice domain, including operational procedures.

@mins, In my opinion, this question may not seem to have a "best answer" because the problem itself is not being actively solved by todays aviators. They don't need to solve it, because it isn't a problem at all if humans stay alert and stick to protocol. That makes it seem like this question doesn't even need to be answered, but if this topic were to become a bigger priority, I am confident that a solution similar to J. Hougaard's would be looked into.

@mins, Not sure what you are getting at, but it is not my opinion that radio interference was part of the Tenerife accident...There is no way around it. At first, my question did seem to fall along the lines of "radio interference caused this great disaster, why isnt it fixed?!?!?", but after seeing that it is never the primary cause, I ammended my question to better suit the idea of a theoretical solution.

It's obviously possible to eliminate this sort of interference, since cell phone systems do it.  (You can hold e.g. conference calls with no problem.)  The real problem would be in getting everyone to change out their equipment.

@jamesqf: Correct, these techniques are not new. 4G uplink (phone to base) uses "single-carrier FDMA", an implementation of the principle known as "direct-sequence spread spectrum" (DSSS), which combines multiple access to a single frequency and efficient use of the medium. This is similar to a WiFi -n channel, or multiple video programs on cable or optical fiber and GNSS. Notice that this is relevant for digitalized signals only.

Firstly, it is worth noting that the blocked radio transmission is only one point on a very long list of factors that caused the horrible accident on Tenerife. There is enough redundancy in aviation systems and procedures that a single fault somewhere in the system will [almost] never be enough to cause an accident. Weather, stress, a terrorist attack, company policy, poor CRM and many other things were also contributing factors.
Communication between air traffic control (ATC) and pilots is mostly based on simplex radio. Simplex radio only allows one station per channel to transmit at the same time; if two stations transmit at the same time, the signal will be blocked. Sometimes, if one signal is stronger, it will be possible to hear that signal but not the other. The main problem is that the two stations transmitting will have no way of knowing that they are blocking eachother. This limitation regularily results in various incidents - for example, when there are two aircraft with similar sounding radio callsigns on an ATC channel, one crew might mistake an instruction for the other flight, thinking it is actually meant for them. If both flights read back the instruction at the same time, neither of them will hear the readback from the other aircraft and realise the mistake, and ATC might hear just one of the readbacks, and not realise that both flights are following the instruction meant for just one of them.
So why isn't there work being done to phase out simplex radio in aviation?
There is. It's called CPDLC, or Controller-Pilot Datalink Communications. (Other, similar systems exist as well, with different names. In the following I will just discuss CPDLC).

CPDLC is a digital system that allows ATC and pilots to communicate via text. It is already widely deployed in many areas, one example being Maastricht UAC, one of the busiest area control centres in Europe. Multiple stations can transmit at the same time, without the risk of blocking other transmissions.
So why do we still have simplex radio?
So far, CPDLC is only used for area control. In areas where ATC instructions are time critical, such as an approach or aerodrome environment, we still rely on simplex radio, because it is guarenteed to be instantaneous - and pilots are used to acting immediately to a voice instruction. However, it should only be a matter of change of procedures and appropriate training before CPDLC can be used in all phases of flight.
More importantly, aircraft equipment is expensive. Replacing a simplex radio with CPDLC equipment involves a significant cost per aircraft. While this may be feasible for large airlines, remember that they only make up a part of flights. There are thousands and thousands of private planes, balloons, gliders and whatnot, and private pilots or flying clubs may simply not have the funds to implement CPDLC. And obviously, ATC can't turn off their simplex radio until everyone has equipment to replace it.
Another disadvantage of CPDLC, or other communication equipment that allows direct communication between cockpit and controller working position, is that it reduces situational awareness. A big advantage with simplex radio is that everyone has to listen to what everyone else is saying, since you can't talk when someone else is talking. This gives pilots the possibility to establish a mental picture of the traffic around them, which ultimately increases safety. As we saw with Tenerife, the lack of such a mental picture can result in tragic outcomes. However, simplex radio has probably prevented many other accidents, because everyone on the frequency knew what was going on around them. The Providence incident of December 1999 comes to mind as one example among many.
So, is there a solution to radio interference? Yes, there is. Is it easy to implement? No, it is both technically and financially difficult. Will it necessarily prevent accidents such as the one on Tenerife? No; a thorough safety and risk analysis must be carried out before deploying it everywhere.

Thanks, this is what I was looking for. It seems that this technology could be simplified even more to something that even can work alongside traditional radio technology. Maybe something that would read the pilots/ATC calls and voice translate them to text, then send them out to others on that frequency.  Being able to have a somewhat accurate text log that one could look back on seems very plausible to me. Definitely not with the current state of antiquated private aviation, but maybe sometime in the distant future.

Even better, once you have digital data link, glass cockpit, and computerized ATC, in theory it should be possible for the display to show the surface radar view that ground controllers sees, and for these display to be annotated with all aircraft's clearance statuses. Much easier to digest than radio comms even with proper phraseology,  far better situational awareness, and the radio would be reserved to relaying non standard information (e.g. debris, aircrafts not showing correctly in radar).

In my experience, airlines are not apt to spend money on avionics upgrades. I'm not saying they don't, but the most likely response is, "We're retiring those planes in five years, so we're not going to spend that kind of money." The GA fleet is hard pressed to require as well because, money. This one issue is (IMHO) the biggest obstacle in aviation equipment modernization.

This isn't really an answer, but it got to be far too long to put in the comments...
Two paragraphs later in the same Wiki:

After the KLM plane had started its takeoff roll, the tower instructed the Pan Am crew to "report when runway clear." The Pan Am crew replied: "OK, we'll report when we're clear." On hearing this, the KLM flight engineer expressed his concern about the Pan Am not being clear of the runway by asking the pilots in his own cockpit, "Is he not clear, that Pan American?" Veldhuyzen van Zanten emphatically replied "Oh, yes" and continued with the takeoff".-Wikipedia, emphasis mine

Not that a technology solution wouldn't be good, but this is the accident that really drove the development and adoption of CRM and standardization of radio phraseology, which, had it been in place at the time, may have had a very strong chance of preventing the incident in the first place.
There were so many factors leading to this particular accident that the interference was only one issue. While it was very important, it wasn't the final bit of communication, wasn't the last thing that was said, and wasn't the last opportunity for the KLM flight to abort takeoff.

Learning that the standards were raised after this incident seems like solution enough for me. I will mark as answer if no better ones show up soon, thank you.

Thanks. Waiting a day or two for a better answer is definitely a good idea!

Also, nearly every accident, especially the fatal ones, drives some sort of improvement in the airline industry.

Yes, this is possible with technology, but there is a big problem too. How do you decide which radio has priority?
Right now the system is "whoever has the strongest signal, wins", but both will probably hear a squeal. ATC may hear both, but the strongest one will probably be audible over the noise. This can be advantageous for example if an aircraft in the pattern needs to declare an emergency while ATC is talking to somebody on long final.
The current system, while antiquated, does work for the most part. There are very few examples of accidents caused by missed communication due to being stepped on by another aircraft. Usually there is more to it, for example in the Tenerife accident the pilot was anxious to get going and ignored the flight engineer's warning about the Pan Am aircraft not being clear. As Freeman pointed out this is where CRM broke down, not the radio's. The other contributing factor in this accident was ATC's inability to monitor the traffic on the ground because of fog and no ground radar.
In the United States there is an active push to reduce commercial radio traffic by using in-cockpit displays to relay ATC instructions. This system relies both on the new ADS-B mandate being in place as well as regulations for equipment being installed in aircraft that can display and alert pilots.

I think the last paragraph is the key to this. It reduces the radio chatter and incorrect readbacks, but it also allows for absolute confirmation as to whether you have clearance or not.

@TomMcW My audio panel also has a "playback" button that can play back the last 3 transmissions. I'm not sure how well it works in really busy airspace since it doesn't distinguish messages meant for you or just chatter on the frequency.

That heterodyne squeal provides an indication to everyone on the frequency that someone was stepping on someone else.  The response to the squeal should be "Say again".

@Gerry:  Radio reception is not always symmetric:  When two receivers are located in different places, one may hear a conflict and squeal, while the other may receive just one transmitter.  Just because one radio picks up a "step-on", does not mean that another radio will.

@abelenky, but the stations that didn't pick up a "step-on" missed at least one of the transmissions and therefore it is still appropriate to request a repeat.

It's worth noting that any solution to the question you raised would not have prevented this, or similar disasters, from happening.
Regardless of any missed or corrupted transmissions with two people speaking at the same time, the crew commenced the take-off without having received, and read-back, a clearance to do so.  Short of replacing humans entirely with computers, there is no solution to a pilot ignoring the established and regulated procedures, put in place to avoid exactly this problem.
The procedures also include the phrase "say again" if you did not hear clearly and simply asking if you have clearance if you have not positively received and understood it.
This disaster was caused by crew error driven by "gethomeitis" and not any problem inherent with radio communications.

I know the Tenerife disaster was caused primarily by the pilot's inability to wait for clearance, and then report it back, but this question is about radio interference and if a solution exists, not if fixing radio interference is a worthwhile task to begin with. Thank you for the "get-home-itis" link, very useful! I have edited my question to remove "Why", as you and others have proven to me it is very very rarely the primary cause of an accident.

I would say not rarely, but never. The primary cause of an incident such as this is human failure. Lost or garbled comms can only ever be a contributing or secondary factor. You could fix the problem you ask about, at great expense and introducing something else to go wrong, and have exactly the same outcome for a new problem (radio failed, crew didn't know), misunderstood since English not first language and so on. Make something idiot proof and someone will just invent a better idiot. The procedure of positive clearance and readback catches them all. Without it, you do not enter the runway.

I agree that proper positive clearance and readback catches all. Sadly, that is not how the real world works, and humans succumb to laziness, fatigue, and other things which cause breakdowns in the procedure. That is why at least to me, it is important to explore any and all possible improvements in regards to the entire overlying system.

It's called Human Factors. Breakdown of proper procedure should not be punishable by death.

There are new ATC radios that have "Detection of Simultaneous Transmissions" or DsiT that alert the controller that more than one aircraft is transmitting.  R&S's Series4200 is one of them.  The controller will get a visual alert on the voice communication system display.

Not that the horrible sound in their ears doesn't alert the controller already...

@UnrecognizedFallingObject: I think in most cases what's needed would be an indication for the person transmitting that their signal is likely not being received.  An automated system that would detect probable signal stomping and transmit a warning signal on a channel reserved for that purpose, along with receivers that would monitor that channel and alert if a signal was received on it related to a current transmission would seem like a simple remedy which should not affect compatibility with existing equipment.

I don't know if this exists in aviation radios, and it would not help if both operators keyed at precisely the same time, but on many amateur radio transceivers (even $35 Baofengs), there is a feature called "busy channel lockout" (BCLO) or something similar. If someone keys their radio, and you try to key up right after they do (not realizing that they have keyed), your radio will refuse to transmit. This prevents accidental interference with another station. However, if a station with BCLO keys first and a station without it keys afterward, the interference will still occur; everyone on the channel has to have BCLO supported and enabled for it to work optimally.
BCLO has a few advantages over DSiT. It is much simpler; it only has to detect a single signal (already done by squelch), not determine how many signals there are. It also prevents interference, rather than just detecting it.
Basically, DSiT does this, when a signal is received:
if moreThanOneSignal() { // complicated (expensive!)
    turnLightOn() // interference still happens, ATC just knows about it
}

While BCLO does this, when the pilot keys the mic:
if atLeastOneSignal() { // very simple, already done as part of squelch circuit
    dontTransmit() // interference is avoided completely; the first station to transmit is heard
}

This (well, effectively the same thing) was already mentioned 5 years ago.

@FreeMan DsiT tells ATC that two aircraft are transmitting. BCLO prevents the airplane's radios from keying if someone is already transmitting. DsiT detects interference; BCLO prevents it.

BCLO also has the advantage that it is simpler and therefore probably cheaper; it only has to determine if there is already one signal or more (already determined by squelch), whereas DsiT has to analyze the signal to see if there is more than one.


text:
What is the minimum and maximum altitude reading for the average radar altimeter?
The valid range for latitude is -90 to 90 degrees.  The valid range for longitude is -180 to 180 degrees.
I previously thought the minimum and maximum altitude reading for the average radar altimeter was 0 to some very large positive number in meters, however, I recently read altimeters (and even other avionics instruments) can display negative altitudes.
What is the minimum and maximum altitude reading for the average radar altimeter?

Why the downvotes?  This question is copy/paste from a previous SO question with over 300+ upvotes except I'm asking for the valid range for altitude rather than something else.

@mins I tagged air-traffic-control so I assumed (incorrectly) that readers would know I'm looking for the upper and lower bound altitude for an aircraft flying under ATC.  I can edit the question to be more specific, perhaps What is the minimum and maximum altitude reading for the average radar altimeter?

Thanks @mins.  Question has been edited.

Did you consider that maybe the downvotes are BECAUSE you copied and pasted?!  Not all questions translate well across all subjects…

I previously thought the minimum and maximum altitude reading for the average radar altimeter was 0 to some very large positive number in meters, however, I recently read altimeters (and even other avionics instruments) can display negative altitudes.

What is the minimum and maximum altitude reading for the average radar altimeter?

Radioaltimeter and radar altimeter are synonymous. I use radioaltimeter.
There are two points in your questions:

What are altitude and an altimeter?
What are height and a radioaltimeter?

Altitude
This is the height above the mean sea level. It can be positive or negative, and altimeters can show negative values as required. Altimeters are based on a measure of the ambient pressure, which decreases with altitude. That's the trick. There are now other means to know the altitude, but for aircraft this is a measure of the pressure and an equivalence in a model.
There are many places on earth below the level of the sea, and some where aircraft can fly.
Height
A height is a distance to a reference. Without other mentions, height is the height above the ground level (termed AGL). Altitude is a special case of height, where the reference is the sea level (termed AMSL).

A radioaltimeter measures the height above the "ground". Ground can be land or sea, depending on what you're flying over at the time of the measure.
A height is positive, as you can't fly under the ground or under the sea.
An interesting case for this answer is what instruments read when flying at a place below the sea level. Let's imagine a place where the ground is at an altitude of -150 ft, and the aircraft flies 100 ft above the ground:

The altimeter will indicate a negative value, -50 ft, as we are 50 ft below the level of the sea.
The radioaltimeter will indicate a positive value, +100 ft , as we are flying at a height of 100 ft above the ground.

Therefore a radioaltimeter will always show a positive value, and zero when on the ground. For accuracy sake, the exact value when on the ground depends on the location of the radioaltimeter antennas and how the instrument is calibrated, in some cases it can be a few meters positive or negative (values less than -20 ft will not be displayed), this detail is not relevant for the principle, you can assume zero.
You can see a radioaltimeter as a laser distance meter. Instead of using an optical ray it uses a radio ray. A radioaltimeter stops measuring height after about 2,500 (some manufacturers extend the limit, up to 6,000 ft). It's mostly used for landing.

To answer your questions:

Altitudes flown in commercial aviation vary from -1,240 ft to +60,000 ft (that was the altitude Concorde flew).

Heights displayed from -20 ft to 6,000 ft (usually 2,500 ft).

Note that the radioaltimeter can be slightly negative: Why does a radar altimeter show negative values on the ground?

Hello mins, great eloborated answer, as usual. I want to add that the radio altimeter can read negative values. The thing is calibrated such that under typical slight nose-up attitude at landing it reads 0 when the main wheels touch the ground. When the aircraft is firmly on the ground, the landing gear struts are compressed so that the indicated height can be slighltly below zero. The radar antenna is usually under the wing and if the outgoing radio signal is reflected at the end of the antenna cable (e.g. because of corrosion) the radio altimeter will read quite a few feet negative.

... for example, in case of the Turkish Airlines flight 1951 crash, a corroded antenna connector caused a radio altimeter reading of -8 ft

I see that @StephenS caught the omission of a key digit in your example…. ;)

@DeltaLima: Always a pleasure to read your interesting additions. Thanks. I've read the related portions of the report. It's a frightening case actually. The cause of the -8ft indication was left undetermined, though connectors problems have been observed and highly suspected. I'm quite surprised the faulty height was still tagged "usable" by the computer, while this was a very sudden and improbable change.

@MichaelHall: Yes, and I wanted to thank him if he reads. Quite confusing figures without his fix.

@mins Happy to help.


text:
Do I need Customs clearance to fly an N-registered aircraft from Italy to Switzerland?
I need to fly from Italy to Switzerland in my aircraft with N markings.
I've been told I need a clearance from a customs office within an airport prior to crossing the border. Is this true?

It's true. You need to take off from a authorised Airport with customs in Italy and land at an airport with customs in Switzerland as your first stop.
Here is all information you need including a list of airports with customs.
https://www.ezv.admin.ch/ezv/en/home/information-private/waren-anmelden/einfuhr-in-die-schweiz/warenanmeldung/grenzueberschreitende-fluege.html

It's not to do with the N-markings... ANY aircraft that wants to fly between Italy and Switzerland needs to fly between 'Customs airfields'. Note - you don't need permission from Customs, just to leave and enter via a Customs airfield, reporting to Customs at those airfields.


text:
Could maintenance data be downloaded via ATC facilities?
Could aircraft send maintenance data to the airport via ATC facilities (e.g., tower, TRACON, enroute)? Or are they only used for air traffic control?

Can you expand a bit on what you mean? What sort of maintenance requests? And what do you mean by ATC "facilities", do you mean ACARS?

By Maintenance data I mean the data that the airline or manufacturers may need for the plane maintenanc when the plane is on the ground. By  ATC facilities, I mean the ground stations that control the plane when a plane enters a new domain such as TRACON, enroute. I don’t know the technical name.

Not through ATC.  The airlines have "company" frequencies they can use for such data.  Outside of airlines, General Aviation can use FBO frequencies for the same communications.

Thanks. Through what facilities are these dara downloaded? Through tower near the airport? Hardware transfer? Or are there other facilities that the data can be sent to before landing?

If it is actual data on the aircraft, it can be transmitted to maintenance over ACARS, I assume.  Normally certain data, such as doors closed/opened at the gate, are transmitted this way for payroll purposes. Normal maintenance information is over voice coms on the Company frequency.  If there is data to be sent, there is agood chance it is more than a burned out light bulb and will require more time on the ground than scheduled.


text:
Are peer-to-peer communications feasible between aircraft?
I have several questions regarding plane-to-plane communications (P2P), by which I mean air-to-ground communications where instead of a satellite, planes act as the intermediate nodes between a given plane and its controller on the ground. Or in other words, peer-to-peer communication.
Would P2P be a feasible model for communicating between ground and aircraft? For example, could ATC or other operational messages be routed to an aircraft using a P2P method? Is this already possible? Does communication with aircraft require a satellite or terrestrial endpoint, or could P2P work instead? How much data and power would be required for all the messages needed for a typical transatlantic flight?

I'm confused. ATC and operational control messages are going to be air-to-ground communications, because the planes are usually in the air and dispatchers are on the ground. Military control situations aside, why would those messages be plane-to-plane?

@ZachLipton I wasn't assuming that ATC is P2P. If you look at my last question it says "Is plane-to-plane communications possible for ATC or AOC TODAY"? I know most of the A2G communications today is via satellite but I was curious to know if any of the communications can be done via P2P? Cause it's a cheaper and more delay-sensitive option.

Welcome to aviation.SE! I reworded your question to focus on what I think is your key point, but it may still be too broad to answer here. If I've changed it too much, don't hesitate to rollback or edit again. You seem to have a lot of assumptions in your question, and I'm not sure how you can say that P2P (which is a general concept or model) is "cheaper" than the radio transmissions used today for air to ground comms. But if you can add more information and be more specific then someone may be able to answer.

Related

@Pondlife Thank you. P2P is a possible option for A2G that's being very actively look at by research community (especially by telecom community). From my what I've read, there are two reasons why P2P is preferable to A2G thru satellite: One is the cost of hardware installation (e.g., the CBB hardware were reported to be as high as $500,000 per aircraft) and power conumption and the other is the propagation delay which is around 240 ms.

What makes you think that the P2P hardware would be cheaper ?

@Antzi I'm not sure. But from what I've read on the Internet, almost everyone unanimously says that P2P is being looked at because communications through satellite is expensive.

This sounds more like mesh networking than peer-to-peer to me. Since planes and ATC aren't peers, isn't any communication between them, regardless of how the communication is relayed, inherently "client-server" with planes being clients and ATC being the server?

Yes, this we could do this.
Actually, we already do it: If an airplane cannot be joined by ATC, ATC will ask planes in the neighbourhood to relay the message.
As for what you are actually asking, which is a P2P mesh network for data or ATC, without active pilots involvement, this could work but would be completely impractical:
Mesh networks are still an active research topic (i.e., not exactly production ready), and offer little to no advantage over a traditional communication (satellite, aircraft to ground) that nobody would bother implementing this.
Few of the downsides are:

What if there is no plane to relay the message ? You are back to P2G (Plane to Ground), so why not use P2G in the first place.
What if there is a broken/rogue airplane that blocks/modify/fake your messages ?

Comments are not for extended discussion; this conversation has been moved to chat.


text:
What helicopter is this in The Walking Dead?
The reason I am asking this is because I want to do a 3D model of it. You can see it in this screenshot from The Walking Dead. At first I thought it was a UH-1H, but the main rotor doesn't look anything like a UH-1H main rotor.


text:
Could I use a powered parachute to fly around New York City?
NYC traffic is so horrendous that it would be pretty convenient to be able to take off with a powered parachute (PPC) from the top of a building or from a park and be able to fly above all the traffic to your destination. I'm wondering if anyone has any insight into this.
I know the class B extends to the surface in upper Manhattan but how about downtown? Class B starts at 1100' (plenty of space for a PPC); could one fly around there without talking to anyone? Also, could one potentially get a class B clearance to fly around at low altitudes in upper Manhattan?
Finally, does anyone know how much space a PPC can take off in? Is there any way a STOL PPC could take off from an NYC rooftop (or more realistically an open space such as Central Park)?
Don't give this question too much thought, just something fun to consider. I think the real limitation would be regs here, even if you could go to the Great Lawn or something to take off.

Wouldn't the random turbulent air flows around buildings be too dangerous?

What exactly do you mean by "powered parachute"? The FAA's PPC Handbook says "A powered parachute can be a single place ultralight
flying vehicle, a single place light-sport aircraft, or
a multi-place light-sport aircraft". That means operating it could be under part 103 or part 91, and those regulations are very different.

Pretty simple, powered parachutes fall under the ultralight vehicle category, which is 14 CFR 103:
14 CFR 103.15 Operations over congested areas.:

No person may operate an ultralight vehicle over any congested area of a city, town, or settlement, or over any open air assembly of persons.

And Also:
14 CFR 103.17 Operations in certain airspace.

No person may operate an ultralight vehicle within Class A, Class B, Class C, or Class D airspace or within the lateral boundaries of the surface area of Class E airspace designated for an airport unless that person has prior authorization from the ATC facility having jurisdiction over that airspace.

It is highly unlikely that you would get a waiver to fly your PPC in the Manhattan Class-B, even if 103.15 didn't preclude it in the first place. You can fly in Class-B in certain areas, but you do need to be talking to ATC.

I don't think there's anything stopping you from registering a PPC as an experimental aircraft, provided it was suitably built by an amateur or designated for R&D.  Then it wouldn't be subject to the Part 103 limitations.  One would have to have a pilot's license in the appropriate category to fly it, and it might still come with FAA-issued Operating Limitations that would disallow flight over congested areas.

I don't believe you can, it wouldn't pass FAA inspections, but even if you could, there is still 14 CFR 91.319: "(c) Unless otherwise authorized by the Administrator in special operating limitations, no person may operate an aircraft that has an experimental certificate over a densely populated area or in a congested airway. " I don't think it's impossible, but companies like Uber have a legal regulation fight with the FAA before they start UAV taxi services anywhere like NYC or LA.

Wait, then how does Iron Man do it?

@Harper Pretty sure Iron Man doesn't obey the laws of physics or thermodynamics, much less the laws of man. Even then, Tony Stark doesn't have much regard for laws anyway, and enough money to pay off whatever bill the government sends him.

A power parachute is a N number plane a powered paraglider Ultralight  so if you are flying to power parachute you can ask for permission  you just need the right type of radio  and a transponder

Welcome to aviation.SE! If you're new to the site you might like to take the [tour] to see how it works. As a Q&A site, we try to find the single best answer to each question, so we generally prefer to see references and sources where possible. In this case, links to the definition of "powered parachute" and the applicable regulations would improve your answer


text:
Does FAA track every plane at every airport?
I use Plane Finder app & noticed they have a “history” area where I can search airspace at a certain place and time.
If I SEE a plane flying, but later check their timeline (on the app), it shows they weren’t flying.

What does that mean?
Is that possible?
Can it mean something was taking place illegally?

Can you give examples of planes that flew and did not show up on commercial tracking sites?

"Can it mean something was takin place illegally?"  No, that's not what that means.

In theory, it's not impossible for this to be an illegal flight? The odds of this are very low considering how many legitimate reasons exist for an aircraft to be flying and not show up on tracking sites... plus as a criminal, hypothetically, why would you do this?

As you may recall from MH370, flying without a transponder, with an inactive transponder, or outside radio range, leaves no track on tracking sites.

The FAA tracks all IFR flights -- those filed to follow instrument flight rules.
The FAA also tracks VFR flights whose pilots request flight following.  This is optional, but commonly done by VFR pilots who are traveling cross country (longer range A to B flights, not short range flights in and out of the same airport).
The FAA does not keep track of aircraft on the ground.  If you have an old photo of an airplane with a tail number, and you want to find the airplane, the FAA can't tell you where it is.

Well, the FAA does also track VFR traffic that isn't using flight following if they're within a area covered by radar, they just don't control that traffic. They still track it in order to prevent conflicts with traffic that they are controlling. And the FAA also typically tracks and controls traffic on the ground if it's on a taxiway or runway at a towered airport. They don't typically track aircraft on the ramp or on the ground at untowered fields, though.

I agree that VFR non-flight-following traffic appears on radar.  However, does the FAA associate an N-Number with it?  I.e. do they identify which aircraft it is?  Perhaps it was just my interpretation, but I took the question to mean "are they following me?...." not "do they know what is in the sky".

Not sure which app exactly you are using, but most flight tracking sites and apps use ADS-B and MLAT to determine a plane’s position (and more).
Both require the aircraft to be equipped with a suitable transponder.
A lot of GA aircraft are not equipped with one and are thus completely invisible on such sites. Even some airliners may or may not be equipped (depends where). Military aircraft may be equipped or not, and may turn it on or off depending on the mission, or even during different parts of the mission. Other specific aircraft (like emergency services, firefighting aircraft…) also may or may not be equipped.
So a plane could very well be in the air and not show up on those apps and sites.
On the other hand, in some airports you may be able to see some ground vehicles which will never get off the ground shown on the maps, because they are equipped.

Plus, some aircraft (military, government) may be equipped and with the transponder turned on, but some sites (esp. FR24) intentionally hiding the flight from display. (And the flight being visible on other tracking sites, or by using your own ADS-B receiver.)

@Mormegil Ah, I didn't know about that. Is that documented or do you know of specific cases?

Sure, it’s not secret, FR24 explains it e.g. at https://www.flightradar24.com/how-it-works#blocking

@Mormegil And that also applies to private aircraft that have requested for their aircraft to not show up on those sites (FR24/FlightAware.) (Though that 'other' site still shows them.)


text:
How is a new airport certified or approved to operate by international organizations?
I just read the news of a new airport in construction in Mexico (Mexico City). They seem to be starting operations in a few months.
In this case, researching a bit, it seems domestic and a Venezuelan airline already had flights to and from that location, and I think only Aeromexico refused to change the hub.
I don't know if the airlines are fined or issued an admonition for landing in a  aerodrome/airport, AFAIK without certification. IMHO, this is risky thing to do.
It reminds me of HKG being transferred from Kai Tak to Chek Lap Kok, but it was a smart idea since the former HKG was amidst a tall buildings zone.
In the case of Mexico's new terminal, there does not seem to be a practical reason to make a new one in the area.
So it makes me wonder: How is a new airport certified by ICAO/IATA/EASA/FAA?
Researching a bit more, this new airport was done scrapping a former project to build terminals 3 and 4 on the actual MMMX (I don't understand Spanish that well, but there is allegiance to turmoil rubbish to do so). The navigability studies were made by NAVBLUE.
And this is an already in operations air force base with a number of operations of that is been retrofitted to admit commercial planes,
Thus it makes me more curious to my question.

Related: https://aviation.stackexchange.com/q/92329/35166

The airport is regulated in general use by the local authority. The local country will designate some airports for regular customs and immigration services. There is a tiny airport near me that is designated as an "international airport" and has regular customs personnel but the runway is too small for any airline. (3000ft/900m long and 60ft/20m wide, surrounded by trees too).
Airlines individually approve each airport that they intend to use regardless of other airport regulations. Each airline has its own set of researched and approved runways, approaches, pilot training, weather conditions, times of day or night, and aircraft combinations. They do many calculations before they ever schedule a flight to know if the airport is suitable for their specific operation.
Airlines file paperwork with border control before the flight which includes the intended airport of landing. Also by the treaties of the Chicago Convention international aircraft are allowed to land at and take off from any public airport for purposes of fuel and maintenance. However, this does not give permission to load or unload pax/cargo or for the crew to leave the airport by ground.


text:
Why does it feel like a plane stops in mid-air during approach?
At some stage while on approach to an airport in a commercial jet, it feels like the plane is almost coming to a complete stop in mid-air. Is this maybe as a result of the flaps engaging or the landing gear creating drag?

I don't think those answers address the question.  The sensation of stopping comes from the deceleration from the thrust reduction plus the beginning of the descent pitchover. Both effects happen when the airplane captures the glideslope and starts on down, and that plus the sound dropping with the thrust reduction creates the sensation/illusion that you are no longer moving.

I agree, the linked answer does not really answer this question. I voted to reopen.

Lowering flaps and gear will add significant drag, which causes the plane to decelerate. Your body feels that, but without visual reference to the ground, your brain has no way to know what speed it was traveling before or after that deceleration.
This is an example of “spatial disorientation”, where the brain gets confusing inputs and comes to the wrong conclusion about what is actually happening. Pilots have instruments to tell us what is actually happening, which we are trained to trust over the suspect data our bodies are giving us, but passengers don’t have that advantage.


text:
What is this probe on the Airbus A330 engine nacelle?

What is the purpose of the little probe seen under the A330neo?

On the Rolls-Royce TRENT 7XX-8XX and RB-221-5XX, that is the "Engine Breather Outlet".

Cite: https://www.scribd.com/doc/283987010/A330-ATA-71-80-RR-Trent-700-L3-e-pdf# (page 44)
Possibly relevant: What is the function of the protruding outlet on the Trent XWB?

So this would be almost similar to the long breather tube on the 737 CFM56.


text:
Did Malaysia flight 370 have a ELT on board?
Couldn't be ELT be used to track its position? And don't airliners have ACARS to identify a crash?

Yes, the aircraft (9M-MRO) flying MH370 had 4 Emergency Locator Transmitters (ELTs) on board according to the final report:

9M-MRO had four ELTs installed. They were located as follows:

One FIXED ELT located above ceiling of the aft passenger cabin [...]
A control switch installed in the cockpit (flight deck) aft overhead panel
provides the command signal. This switch is guarded in the ARMED
position. If required, the flight crew can select the ELT to ON by moving
the guarded switch from ARMED to ON. [...]
The ELT will activate
upon a sudden deceleration force per the Technical Standard Order. [...]

One PORTABLE ELT located in the forward cabin right hand coat
closet.
This closet is used by the cabin crew. [...]
The portable ELT has a control switch on the front face. It is normally
in the OFF position. When needed, the switch can be selected to the
ON position to activate the ELT transmission. [...]

Two SLIDE RAFT mounted ELTs located at Door 1 Left and Door 4
Right (packed within the slide raft assembly). [...]
The slide raft ELT is automatically armed when the slide
raft is deployed and inflated. Once armed the ELT is automatically
activated by a water sensor coming in contact with water. [...]

No relevant ELT beacon signals from the aircraft were reported from
the responsible Search and Rescue agencies or any other aircraft.

(SAFETY INVESTIGATION REPORT - Malaysia Airlines Boeing B777-200ER (9M-MRO))
To answer your specific questions:

Couldn't be ELT be used to track its position?

No, the ELT is not normally transmitting anything, it is for emergencies only. As you can read in the quote above, only the fixed ELT will start transmitting automatically in case of a crash. There is a lengthy analysis in the final report about ELT effectiveness and the use of satellite tracking (have a look at chapter 1.6.7 for more details). As the report says, no signals were ever received from MH370.

And don't airliners have ACARS to identify a crash?

The ACARS is essentially just a network for sending text data via VHF or satellite. MH370 did send several ACARS messages during the first part of the flight. The system has nothing to do with identifying a crash. See chapter 1.9.4 for more details on ACARS for MH370.


text:
What would happen if an airplane climbed beyond its preset cruise altitude that the pilot set in the pressurization system?
What would happen? Would the cabin pressure increase too much and cause damage?

In what system do you do that? Normally you just set the destination landing elevation.

@JohnK The Boeing 737 for example.

@757toga Yes, that's correct.

I think the question is basically a good one.  For the 737, we set the Cruise Altitude and Landing Altitude in the controller before the flight.  Then, normally, we take off, climb to that cruise altitude, cruise there, and then descend to the planned destination. And the pressurization controller gives you a cabin altitude that climbs slowly to some determined value (often 8,000' MSL, but not always), stays there during cruise, and then descends gradually to reach (approximately) the destination field elevation at the same time the aircraft is landing.

So what happens if things don't go quite according to that plan?

What if the aircraft takes off, climbs to an altitude below the planned cruise altitude, and then descends?
What if the aircraft takes off and climbs to an altitude above the planned cruise altitude (the point of the OP)?
What if the aircraft takes off, reaches the planned cruise altitude, and descends and lands at a field elevation different than what was entered in the controller?

In the first case, where you descend before reaching cruise altitude, that's referred to as an "Off Schedule Descent" and you'll get a Master Caution > Pressurization light, and an amber light on the controller.  The controller is designed to, in this case, assume that you're returning to your departure field, and it recomputes the cabin altitude schedule so that the cabin will now reach the departure field elevation at the same time that the aircraft reaches that altitude.  This means that in the case where you take off, have a problem, and return to land at your departure airport, you can cancel the Master Caution and everything will do what you want.  (If you decided to divert to an airport with a different elevation, then the checklist would direct you to set the field elevation of the new destination in the appropriate window, and all would work fine from there.)
In the case where you climb above the cruise altitude, the controller will handle it in such a way that you neither exceed the max cabin differential nor exceed a 10,000' cabin altitude.  In the case of the 737 NG and Max, the cabin can be maintained at 8,000' at the aircraft's 41,000' ceiling without exceeding the max differential, so regardless of what combination of differential and cabin altitude was planned at the original cruise altitude, there is leeway to climb up higher without anything bad happening to the cabin.  If the original cruise was at 25,000', you probably had both a lower cabin altitude than 8,000' and a lower-than-maximum differential; climbing from there up to 41,000' (you forgot to set your pressurization controller between the short-haul flight and the long-haul leg!) will probably bring both toward what they'd be anyway when cruising at FL 410, although perhaps not as smoothly as could be achieved by setting things up correctly at the start.
If you land at the "wrong" field elevation, either you'll land pressurized  or you'll "catch the cabin" and the last some bit of the descent will be unpressurized.  The former could happen if you landed in DEN while the controller was on a schedule to reach a 0' cabin altitude as the airplane lands at sea level, for instance, so the cabin is pressurized to nearly sea level as you're landing at 5,000'.  The latter scenario would be the reverse, where the controller expects to land at 5,000' but you're actually landing at sea level, so at 5,000' the differential is basically zero, and then as you descend lower the cabin is descending as rapidly as the aircraft is (i.e. you're unpressurized below 5,000').  That wouldn't be as comfortable for the people on board as you'd like, since descents at 1,500 feet per minute are typical for a clean 737 descending at idle and 250 knots, but the cabin typically climbs and descends at around 300-500 FPM.  The higher rate isn't dangerous (unless somebody is flying with a head cold -- that case can pose risks for ears and sinuses), but it's a lot more ear-popping than normal.
Landing pressurized is undesirable, because (by design) aircraft doors are hard or impossible to open when there is significant pressure differential, and if you do get one open then there can be a pretty strong burst of air rushing out the now-open door, which in the worst case can be dangerous for whoever is opening the door. To avoid that scenario, once the aircraft has "weight on wheels" the outflow valve will drive fully open to depressurize the cabin quickly, and that can be a bit of an ear-popping change in pressure too.
But in all cases, things should keep you safe and avoid any situation reaching or exceeding an operating limit (such as the max pressure differential).  There are pressure relief valves that open to protect the fuselage from exceeding the limits, but if the controller is working correctly, it will control the differential so that even that relief valve won't need to open.

This was truly an abundance of information. Thank you very much!!!

"Landing pressurized is undesirable" - Generally you want to have a slight positive pressure on take off and landing for increased hull rigidity. Especially on the 737 you can feel the pressure slightly but quickly increasing when t/o thrust is set.


text:
What are those pylon looking things on the rear of this DC-8 wing?

(image source: airliners.net)
What are those humps on the rear of the wing? Are they external fuel tanks?

That's not a DC-8, it's a Convair 990,and those 'humps' are anti-shock bodies.

You are looking at a Convair 990 Coronado and not a Douglas DC-8 aircraft.
For a direct comparison look at the image below. The Convair 990 has, compared to the DC-8, more windows that are more closely spaced. Also, when you look at the cockpit windows, the DC-8 has eye-brow windows while the Convair 990 lacks them. In the image you posted you can clearly see the distinct trapezoidal entry doors (wider at the top than at the bottom) of the Convair while the DC-8 has the usual rectangular doors. The most obvious difference are the "humps" on the wing of the Convair

Douglas DC-8 (left) and Convair 990 side by side (Source: Wikipedia)
The "humps", as you called them, are anti-shock bodies designed to reduce wave drag when traveling in the transsonic speed regime. The idea behind it is to keep the cross section constant over the length of the aircraft and smooth out cross section area changes. This is known as the application of the area rule.

Weren't they called 'speed bodies' in Convair publicity?

@MichaelHarvey I'm not aware of the nomenclature Convair used in their public relations material. The anti-shock bodies are also known as Whitcomb body, Küchemann carrot or speed bump. Richard T. Whitcomb (NASA) and Dietrich Küchemann (RAE) being the namesakes.

You forgot the most important difference: The DC8 smiles!

@RetiredATC I've never seen it like this – you're right! Not as broad as a B747F though.


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How to calculate lift and drag of commerical aircraft in different phases of flight?
What is the best way to mathematically calculate values of lift and drag forces, in different phases of flight: takeoff, climb, cruise, descent, and approach?
Edit: I have the idea of calculating the lift force by using the information of speed and angle of attack (for the coefficient of lift value) in different flight phases from the pilot's "flight manual" (if it is obtainable there), in standard ISA conditions L=CL*(r+v⌃2/2)x wing area. For drag, I would use same inf. and the total drag coefficient is equal to the drag coefficient at zero lift, plus the induced drag coefficient Cd = Cd0 + Cl^2 / ( pi * Ar * e), where The efficiency factor (e) is equal to 1.0 for an elliptic distribution and is some value less than 1.0 for any other lift distribution. –

So lift and drag are properties directly proportional to the angle of attack (AoA) of the aircraft.
The equation for lift and drag of an airfoil would be:

L=N*cos(phi)-Asin(phi)

D=N*sin(phi)+Acos(phi)

N and A represent force in the normal direction and in the axial direction respectively.
And N is dependent on the pressure on the airfoil, while A depends on the shear stress on the airfoil.
So if given the airfoil parameters, AoA, pressure, and shear stress, you can calculate the lift and drag.

Moreover, if you are given the lift and drag coefficient, you would simply use the equation

C_{L}=L/(q_inf*S)

C_{D}=D/(q_inf*S)

and q_inf here denotes the dynamic air pressure far away.
The equation for q_inf is q_inf=1/2rho_infV_inf^2.
And as you may have guessed, rho_inf is the density far away and V_inf is the free stream velocity far away. (This equation is very similar to 1/2mv^2)
And S in this case is the surface area of your airfoil, or more generally speaking, the size of your object.
I hope this helped a little :)

You probably mean alpha not phi